The problem (as far as i understand) is that u set the variable to 1 if the switch is pressed.Now in my experience u dont want to "set" the switch to 1.Because construct2 recognises u pressing the switch even after it has set that variable.The result is this:

Pressed switch --> set variable to 1 --> set variable to 0

So when u then hit the arrow on screen, u go to Room B.

To make switches using variable i always do the following.I came up with this method after having the same problem long time ago.